Apparatus for separating and measuring gas in drilling fluid

ABSTRACT

Apparatus is provided for use in wells, allowing the well to be drilled with minimum hydrostatic head and yet insuring against the possibility of blowouts, and for measuring the gas flow rate from a separator which includes a plurality of parallel pipes of differing sizes. Each pipe has a flow rate detector, and suitable valves are included for passing the gas flow into whichever pipe is desired, depending on the flow rate. If the flow rate is great, a large pipe is used; if the flow rate is small, a small pipe is used.

Ol-l1-72 OR 3%)339687 Ullltu uuwwu l .ll [H] [72] Inventors AlfredGordon West [56] References Cited 3 81: d 501 sch M D UNITED STATESPATENTS 2 082 329 6/1937 Foran et al 175/48 Clyde E. Perce 600 Lidon,all of Midland Tex 7970] 2,700,897 2/1955 Arps 175/50 X [21) Appl. No.884,502 Primary Examiner- Ernest R. Purser [22] Filed Dec. 12, 1969AnorneysAmold, Roylance, Kruger & Durkee, Tom- [45] Patented Jan. 11,1972 Arnold, Donald C. Roylance, Walter Kruger, Bill Durkee,

Continuation-impart of application Ser. No. Frank vaden, and Louis670,559, Sept. 26, 1967, now Patent No.

498 393. This Ii ti D 12 1969, 3; 884 ca on cc ABSTRACT: Apparatus isprovided for use in wells, allowing the well to be drilled with minimumhydrostatic head and yet insuring against the possibility of blowouts,and for measuring [54] APPARATUS FOR SEPARATING AND MEASURING the gasflow rate from a separator which includes a plurality of GAS IN DRILLINGFLU") parallel pipes of differing sizes. Each pipe has a flow rate de- 4Claims, 2 Drawing Figs. tector, and suitable valves are included forpassing the gas flow into whichever pipe is desired, depending on theflow [52] U.S. Cl 11775724086 raw If the flow rate is great a large pipeis used; if the flow 51 Int. Cl ..E21b21 0o, me Small a used E21b 47/00[50] Field of Search 175/29, 38,

' trol.

APPARATUS FOR SEPARATING AND MEASURING GAS DRILLING FLUID REFERENCE TOOTHER APPLICATIONS flhis application is a'continuation -in-part of ourcopending BACKGROUND OF THE INVENTION One of the most critical problemsin drilling an oil or gas 7, well into the earth is the tendency to losepressure equilibrium under certain well conditions, resulting inblowout" of the well. A blowout is the wasteful blowing of oil and gasout of the well and the complete loss of control of pressure. In view ofthe tremendous capital investment necessary to drill a well (drillingcosts often run to many hundreds of dollars per day and the drilling hasoften been proceeding for many days when the greatest risk of blowoutoccurs) it is seen that a blowout is almost always an enormouslyexpensive thing. In addition to the expense involved, a blowout is oneof the most devastating and destructive things that can happen to awell; wells which have blown out are almost always damaged (damage whichmay be realized throughout the life of the well), and often must becompletely abandoned. Even if the well can be brought under control, agreat deal of time is often lost in drilling and special equipment andextra labor (which may not be readily available) are needed to bring thewell pnder con- A still further hazard of the blowout is thatthefriction of the equipment at the well head can be sufficient to causea fire in the blowout gas, and of course such a fire is not onlyextremely expensive but very dangerous to the workmen at the rig, andruinous to the rig equipment.

Blowouts most often occur in formations which contain high pressure gaspockets. In the drilling process a drilling fluid or drilling mud iscustomarily circulated down the borehole to clean the hole of cuttingsand lubricate the drill bit. Blowouts can be prevented by establishingpressure control with this drilling mud. That is, if the pressure of thehydrostatic head of the drilling mud is at all times kept greater thanthe bottom hole pressure of the well, blowouts may be prevented. And thehydrostatic head of the drilling mud can be varied by varying thedensityof the mud, as is well known in the drilling art. Further, thenormal formation pressure of the strata being penetrated may bedetermined by standard methods. Consequently, it is the present practiceto maintain the hydrostatic head at a level considerably greater by somesafety factor" than the normal bottom hole pressure.

There are two grave difficulties with the use of this safety factortechnique. The first is that it does not compensate for the abnormalconditions which sometimes develop, and consequently is only partiallyeffective in preventing blowouts. Secondly, in using the prior artmethods a relatively large differential between hydrostatic head andnormal bottom hole pressure must be maintained, which means that thehydrostatic head is at nearly all times much greater than is reallynecessary.

Maintenance of the hydrostatic head of the drilling fluid at a levelabove what is necessary is in itself a significant problem to thedriller. For example, it has been shown that a lighter hydrostatic headresults in a faster penetration rate. And of course, a fasterpenetration rate is desirable in drilling of wells because of thesavings in time required to drill a well (and hence the cost ofdrilling), realized. Further, a higher hydrostatic head will result ininjury to certain formations which are low in pressure. That is, if thepressure in the borehole is significantly greater than the pressure inan adjacent formation, the formation might be fractured by the drillingfluid in the borehole, thereby permanently injuring the formation andforever damaging its permeability to thereby result in permanentdecrease of the productivity of the well. Such fracturing is alsoundesirable because a great deal of the drilling fluid can be lost intothe fractured formation. It hasalso been shown that longer bit life isachieved with a lighter hydrostatic head. That is, the bit will not wearout so quickly if the mud weight is decreased. This is extremelyimportant since when the bit does wear out, the drilling must, bestopped and a trip" must be made to replace the bit. This can often takemany hours of valuable downtime on the rig. It also results in a buildupof ftrip gas" during the trip, and this gas further contributes to theblowout problem. For these and other reasons, it is alrnostale waysdesired to drill with the smallest possible hydrostatic head. 1

As hazardous and as expensive of aproblem as it is, a blowout does notoccur instantaneously. Rather, it is something which builds up over aperiod. of time, (a time period which may be short, however, if theformation permeability is great) and then, perhaps is ratherinstantaneous in its result. For this reason blowouts can be preventedand continuous pressure control established by the use of thepresentinvention, while the driller is able to continuethe drillingusing a relatively light hydrostatic head.

SUMMARY OF THE INVENTION The present invention ,provides,apparatus formaintaining pressure control whiledril ling a well such as an oil or gas.well, to thereby prevent the occurrence of a blowout. Such ,apparatusincludes, in conjunction with means for circulating drilling fluid intothe borehole means for separating free gas from the drilling fluid uponits return to the earth's surface, and means for measuring the gas flowrate of the free gas from the separator.

The apparatus for measuring the flow rate of the free gas includes aplurality of parallel pipes of differing sizes. Each pipe has a flowrate detector, and suitable valvesare included for passing the gas flowinto whichever pipe is desired, depending on the flow rate of the gas.As will be more fully discussed below, the size of pipe used isdirectly-proportional to the flow rate, the larger pipes being employedfor the larger flow rates.

BRIEF DESCRIPTION OFTHE DRAWINGS FIG. l is a schematic elevational view,partially in section, of a borehole during the drilling process, whereinthe method of the present invention isemployed; and

FIG. 2 is a side view of apparatus according to one embodiment of thisinvention. I

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS A schematicillustration of a well-drilling operation employing the presentinvention may be seen in FIG. I.

Here it is seen that a borehole. 10 has been drilled into the earthextending from the surface 12 to a point 14 beneath the surface, througha plurality ofdifferent geological formations l6, 18, 20 and 22. It willbe readily understood that as drilling proceeds the borehole 10 will getdeeper and deeper.

The borehole 10 is being drilled in this instance by a rotary drill bit24 suspended at the end of a string of drill pipe or a drill string 26.The bit 24 is rotated by suitable power means 34 located on the derrickfloor 36 at the earths surface. Suitable drill collars 28 may bepositioned onv the drill string just above the drill bit 24 in order toweight the bit and cause it to more effectively drill the formation.

The borehole wall may be protected by the installation of a casing 30 toany desired level in the borehole. In those regions protected by thecasing 30, the problem of fracturing discussed above is overcome.

The apparatus of this invention is useful in connectionwith means forcirculating a drilling fluid which may bewater or oil, but is commonly"mud" (typicallya mixture of clay and water with suitable additives),during drilling, from the surface down the center 32 of the hollow-drillstring 26, past the drill bit 24 at the bottom 14 of the hole,.andthenceup the annular .area 33 outside the drill string between the drillstring and the casing 30 or borehole wall. Means for circulatingdrilling fluid this manner are well known in the priorart.

As the bit 24 is rotated with the drill string by the power means 34, itcuts away at the adjacent formation 22, forming loose cuttings at thebottom of the hole. As the drilling mud sweeps the bottom of the hole,it carries these cuttings upwardly through the borehole to the earthssurface. The drilling mud also cools the bit, and serves to maintain thehole gauge by its continual sweeping action.

But the drilling mud provides another vital function and that is toserve as a balance against the bottom hole pressure to thereby preventblowout. The hydrostatic head is directly related to the depth of theborehole and the density of the drilling mud, by the following equation:

p=0.052dh where p is the hydrostatic head in p.s.i.,

d is the density of the mud in pounds per gallon, and

h is the depth of the column in feet.

Mud density may be regulated by conventional and wellknown methods(literature available from National Lead Company, Baroid Division, forexample) by the addition of weighting additives to the mud before it isintroduced into the borehole, and may be readily determined by suitablemeasurements well known to those of skill in the art. Therefore, it is arelatively simple matter to calculate the hydrostatic head and to adjustthe hydrostatic head to any desired value at all times.

The pressure of the fluid in the pores of a rock formation determinesthe formation pressure" of that particular strata. The variousformations l6, 18, 20 and 22 through which the borehole penetrates existat different formation pressures. Since the normal pressure gradient isknown for the particular area of drilling, the normal formation pressuremay be calculated simply by multiplying the normal gradient times thedepth of the borehole. To balance this formation pressure, the drilleradjusts the hydrostatic head by increasing or decreasing the density ofthe drilling mud as mentioned above. And then to allow for pressuresurges and higher than expected pressures, a safety factor is added;that is, the hydrostatic head is maintained at a value considerablygreater (for example, 750 p.s.i. greater) than the normal formationpressure. This safety factor is necessary because, as mentioned above,the formation pressure varies even within one formation; further, thedrill may suddenly hit a relatively high-pressure gas pocket.

There are at least two principal difficulties with the use of thesesafety factors in present practice, as discussed above. The first andmost critical is that they are sometimes not large enough to compensatefor the extremely high-pressure gas pockets which are sometimesencountered, especially in certain areas of Texas and Louisiana. If sucha gas pocket is encountered and the gas pocket formation is ofsufficient permeability, a blowout may occur. The second problem withthe safety factor practice is that the safety factors used are (for thegreat majority of situations) overly large, to compensate for problemssuch as that just described. Use of these large safety factors meansthat the hydrostatic head is maintained at a level significantly aboveand beyond what is generally needed, resulting in lower bit penetrationrate, shorter bit life, consequent increase in cost of drilling thewell, and the risk of fracturing a low-pressure formation.

ln addition to these difficulties, when it is determined that ahigh-pressure pocket has been encountered (and a blowout has notoccurred), drilling through such pocket under present practice is slowedto a very slow pace, resulting again in increased cost of drilling.

Some formations are known as fhigh-pressure, low-volume" formations.Because of their low permeability, there is no real blowout danger insome of these formations even though the gas exists in the pores of thestrata at high-pressure. This is simply because not enough of thehigh-pressure gas can find its way into the borehole. These formationsare often of no real concern to the driller, as far as the blowoutproblem is concerned, so in some such formations only, the bottom holepressure may safely be greater than the hydrostatic head.

As the drilling mud sweeps the bottom of the borehole, as seen in FIG.1, gas from the formation being cut by the drill bit will enter theborehole and will be returned to the surface up the annulus 33 by themud. Some relatively small amount of the gas will be dissolved in themud, while other gas, which may be termed free gas, will not bedissolved but will be returned to the surface by the drilling fluid. Inaccordance with this invention, when this gas-containing mud reaches thesurface it is transported by suitable means such as the pipe 38 to aseparator 40 suitable for separating the free gas from the mud. Suitablechoke means may be. included in the line'38 to reduce the pressure ofthe mud-gas mixture to a level which may be properly handled by theseparator. In this connection, it has been found particularlyadvantageous to use the twostage system illustrated in FIG. 1,comprising the adjustable choke 84 and the hydraulic choke 86. Thetwo-stage pressure drop efiected in this manner has been found to beeffective in preventing equipment damage due to high gas pressures.

The separator 40, which may operateat any convenient pressure as forexample I25 p.s.i., may be elevated so that the mud may return bygravity through a mud return line 44 to a mud pit 46, for laterrecirculation into the well.

The gas exits the separator 40 through a gas line 42, and is thencemeasured to determine the volume of gas released from the separator.Such measurement may be made in any suitable manner, one example beingillustrated in FIG. 2.

A multiple flow line system which has been found to be particularlyadvantageous for the measurement of gas flow under all conditions isshown in FIG. 2. The primary advantage of this particular system is thatit allows accurate and precise flow measurements for gas flow ratesranging from very high to very low. In accordance with this system,several lines of different sizes are connected in parallel, withinstruments for measuring flow rate positioned in each line. Since it isdifficult to get accurate and precise measurements when there is verylittle flow through a' large line, or when there is large flow through asmall line, the flow is directed by the operator through the appropriateline by suitable flow control means, depending on the volume of flow.

in this embodiment, the line 42 from the separator may be 6 inches indiameter. Parallel line 50 may be four inches in diameter and may besecured by an elbow connector 51 to the line 42 at a point spaced fromthe separator 40. Another parallel line 54, which may be three inches indiameter, may be secured in a similar manner by appropriate elbowconnection 55, to the line 50.

The parallel lines are in fluid communication at a point spaced fromtheir connection with each other, with a transverse line 62 whichcommunicates with a flare 64 whereby the waste gas is desirably burned asafe distance from the rig.

Suitable flow control means such as valves are located at appropriatepositions in the lines, as seen in FIG. 2. Valve 52 is located in line42 downstream from the connection of line 42 with line 50. Valve 58 islocated in line 50, downstream from its connection with line 54. Intransverse line 62, suitable valves 68, 70 and 72 are located betweenline 42 and flare 64, line 42 and line 50, and line 50 and line 54,respectively. A small line 60 for use with very small flow rates may belocated transverse to the parallel lines 42, 50, 54 and secured in fluidcommunication between the lines 54 and 42. This line may be for example3/4 inch in diameter, and may contain an orifice 66 of any suitable sizetherein.

A rupture plate 56 which may be adapted for rupture when the pressurereaches a certain level, for example I00 p.s.i., is located in line 54near its connection with line 50.

Suitable flow measurement means, such as pitot tubes, are

located in the various lines. Tube 74 is positioned in line 42 betweenthe separator 40 and the connection with line 50; tube 76 is positionedin line 50 between its connections with the lines 42 and 54, tube 78 inline 54 between its connections with the lines 50 and 60, and tube 80 inthe line 60 between its connections with the lines 54 and 42, preferablyat the orifice 66. Each of these tubes or other flow indicators issuitable for measuring the flow rate of the gas passing through the linewherein it is located, and suitable means are connected with each suchtube for continuously recording the data received on a recorder 82. lnthis manner, a continual record of the flow rate of gas returning fromthe well may be kept.

The manipulation of the various valves in order to effect flowthrough'ariy of the desired lines is readily apparent by reference toFIG. 2. Thus, when the flow rate is relatively large and flow'is desiredthrough the line 42, the valve 52 is opened and the valve 58 is closed.But if 'flow through line 50 is desired, then the valve52 is closed andthe valve 58 is opened.

Since the'flow rate of the gas released from the separator is, assumingconstant permeability, directly proportionalto the bottom hole pressurein the well, these flow measurements enable the driller to keep aconstant, up-to-the-minute account of what is happening, pressurewise,downhole. And by comparing the flow rate measurements with similarmeasurements taken earlier, the rate of change in the flow rate may alsobe determined. These measurements thus allow the driller to determinewhether a gas zone is depleting or whether additional gas is beingencountered, and thus predict what is happening downhole at any givenmoment. The operator knows when the drilling has proceeded into ahigh-pressure gas pocket. The hydrostatic head is then adjusted whennecessary by decreasing or increasing the density of the drilling mud bymixing with the mud the appropriate additives.

It is still necessary in formatioii's which are not relatively lowvolume formations, to maintain the hydrostatic head at a level somewhatgreater than the bottom hole pressure. It will be recognized that thedifferential employed will vary somewhat depending on the formationsbeing drilled and other factors, but in many contexts of use, it isfound that a pressure differential of about 200-250 p.s.i. issufficient. This is considerably less than the differential necessaryfor safety with conventional drilling processes. And it is thedifference between the hydrostatic head levels which may be utilizedwith the present invention, as compared to those which must be used withprior art methods, which is important-rather than the absolute value ofthese hydrostatic head levels. These absolute values, of course, are toa great extent governed by formation properties. As an example, if it isdetermined that a 250 p.s.i. differential is appropriate for use in agiven situation, the mud density is continually adjusted so that thehydrostatic head is maintained at a level exceeding the bottom holepressure by 250 p.s.i. Complete pressure control is thus maintainedwithout danger of blowout.

When a high-pressure gas pocket is struck, the driller will have timeusing the method of the preset invention to increase the mud densitysufficiently to avoid blowout. This is because there is a delay or lagtime between the bits striking the gas pocket, and any possible blowout,because formations are not sufficiently permeable to cause instantaneousblowout. Of course, this lag time varies greatly depending on thepermeability of the formation and the pressure of the gas pocket, andtherefore it is greatly desired that fairly immediate corrective actionbe taken whenever necessary. This of course is one of the greatadvantages of the present invention.

It is here noted that there are presently methods for determiningbottom-hole pressure, such as that known as the drill stem test. Butsuch methods are expensive, dangerous, and cannot be continuouslyperformed during drilling of the well. If it is desired to take such atest during drilling of the well while the process of this invention isbeing used, then such a spot check will allow the driller to bettercorrelate the data received. For example, if the flow rate isincreasing, the driller can tell just exactly how much of the increaseis due to an increase in bottom-hole pressure and how much is due toincreased porosity of the formation. Such procedures are not generallynecessary however. Since the formation porosity is generally known atleast to some degree, the measured flow rate of the gas returning fromthe well (and the rate of change therein) has been found to give adirect and accurate indication of the bottom-hole pressure picture. Inother words, although the porosity of the formation does have an effecton the flow rate measurements, such effect can usually be discounted togreat extent because of the knowledge the driller will have of theformation being dr illed, and the safety factor allowed.

It is seen that the invention has, provided an apparatus for wellcontrol which providesfor complete pressurecontroh'at all times withminimum risk of costly and dangerous blowout... Further, the inventionprovides an apparatus whichallows for faster penetration rates andlonger bit life', resulting in reduced drilling costs. The apparatus of.the present'invention. also is seen to allow for faster drilling throughstrata wherein the formation pressure is -high,.and to provideprotectionagainst the fracture of low-pressure formations.

It is further .seen that the present invention. provides apparatussuitable for'accurately and preciselymeasuring the flow rate of free gasemanating from the-well, regardless of whether the flow is great orsmalli- The apparatus is desirably portable so that it may be readilytransported form rig to rig.

What is claimed is: i

1. Apparatus for use in connection with the drilling ofwells, allowingthe well drilling to proceed withminim um-hydrostatic head on the columnof drilling fluid while at'the same time minimizing the possibility ofblowout, said apparatus being utilized in connection with means forcirculating drillingfluid through the borehole so that thedrillingffluid'. carries cuttings and free gas from theborehole to theearth's surface, including:

separator means for separating said free gas from said drilling fluid;

means for receiving said free gas after separationthereof,

said means including a conduit: system comprisinga plurality ofgenerally parallel conduits of differingsizes, arranged in a manner suchthat the gas flow maybe directed into any one of said conduits dependingupon the approx imate quantity of said flow; means in said conduitsystem for measuring when desired the gas flow rate therethrough; and,

means for flaring said gas. after it has passed through. said conduitsystem.

2. Apparatus suitable for measuring the flow rate of gas emitted from amud-gas separator, comprising: i

a first line having a selected diameter, in fluid communication withsaid separator;

a second line having a diameter smaller than the diameter of said firstline, in fluid communication with said first line at a point spaced fromsaid separator;

a third line having a diameter smaller than the diameter of said secondline, in fluid communication with said second line at a point spacedfrom the connection of said second line with said first line;

suitable flow control means in said lines selectively directing flowthrough either said first line, said second line, or said third line;

a transverse line in fluid communication with each said first line, saidsecond line, and said third line, and with a flare for burning wastegas;

measuring means in each said first line, said second line, and saidthird line, suitable for measuring the gas flow through each of saidlines;

whereby gas from said separator can be selectively directed througheither said first line, said second line or said third line dependingupon the flow rate of said gas, to achieve accurate and precise flowmeasurements regardless of the volume of flow. 3. Apparatus suitable formeasuring the flow rate of gas emitted from amud-gas separator,comprising:

a first line having a selected diameter, in'fluid communication withsaid separator;

a second line having a diameter smaller thanthe diameter of 7 wherebygas from said separE r can be selectively directed through either saidfirst line or said second line depending upon the flow rate of said gas,to achieve accurate and precise flow measurements regardless of thevolume of flow.

4. Apparatus suitable for measuring the flow rate of gas emitted from amud-gas separator, comprising:

a first line having a selected diameter, in fluid communication withsaid separator;

a second line having a diameter smaller than the diameter of said firstline, in fluid communication with said first line at a point spaced fromsaid separator;

a third line having a diameter smaller than the diameter of said secondline, in fluid communication with said second line at a point spacedfrom the connection of said second line with said first line;

suitable flow control means in said lines for selectively directing flowthrough either said first line, said second line, or said third line;

measuring means in each said first line, said second line, and saidthird line, suitable for measuring the gas flow through each of saidlines;

whereby gas from said separator can be selectively directed througheither said first line, said second line or said third line dependingupon the flow rate of said gas, to achieve accurate and precise flowmeasurements regardless of the volume of flow.

I l 0 III III

1. Apparatus for use in connection with the drilling of wells, allowingthe well drilling to proceed with minimum hydrostatic head on the columnof drilling fluid while at the same time minimizing the possibility ofblowout, said apparatus being utilized in connection with means forcirculating drilling fluid through the borehole so that the drillingfluid carries cuttings and free gas from thE borehole to the earth''ssurface, including: separator means for separating said free gas fromsaid drilling fluid; means for receiving said free gas after separationthereof, said means including a conduit system comprising a plurality ofgenerally parallel conduits of differing sizes, arranged in a mannersuch that the gas flow may be directed into any one of said conduitsdepending upon the approximate quantity of said flow; means in saidconduit system for measuring when desired the gas flow ratetherethrough; and, means for flaring said gas after it has passedthrough said conduit system.
 2. Apparatus suitable for measuring theflow rate of gas emitted from a mud-gas separator, comprising: a firstline having a selected diameter, in fluid communication with saidseparator; a second line having a diameter smaller than the diameter ofsaid first line, in fluid communication with said first line at a pointspaced from said separator; a third line having a diameter smaller thanthe diameter of said second line, in fluid communication with saidsecond line at a point spaced from the connection of said second linewith said first line; suitable flow control means in said linesselectively directing flow through either said first line, said secondline, or said third line; a transverse line in fluid communication witheach said first line, said second line, and said third line, and with aflare for burning waste gas; measuring means in each said first line,said second line, and said third line, suitable for measuring the gasflow through each of said lines; whereby gas from said separator can beselectively directed through either said first line, said second line orsaid third line depending upon the flow rate of said gas, to achieveaccurate and precise flow measurements regardless of the volume of flow.3. Apparatus suitable for measuring the flow rate of gas emitted from amud-gas separator, comprising: a first line having a selected diameter,in fluid communication with said separator; a second line having adiameter smaller than the diameter of said first line, in fluidcommunication with said first line at a point spaced from saidseparator; suitable flow control means in said lines for selectivelydirecting flow through either said first line or said second line;measuring means in each said first line and said second line suitablefor measuring the gas flow through said lines; whereby gas from saidseparator can be selectively directed through either said first line orsaid second line depending upon the flow rate of said gas, to achieveaccurate and precise flow measurements regardless of the volume of flow.4. Apparatus suitable for measuring the flow rate of gas emitted from amud-gas separator, comprising: a first line having a selected diameter,in fluid communication with said separator; a second line having adiameter smaller than the diameter of said first line, in fluidcommunication with said first line at a point spaced from saidseparator; a third line having a diameter smaller than the diameter ofsaid second line, in fluid communication with said second line at apoint spaced from the connection of said second line with said firstline; suitable flow control means in said lines for selectivelydirecting flow through either said first line, said second line, or saidthird line; measuring means in each said first line, said second line,and said third line, suitable for measuring the gas flow through each ofsaid lines; whereby gas from said separator can be selectively directedthrough either said first line, said second line or said third linedepending upon the flow rate of said gas, to achieve accurate andprecise flow measurements regardless of the volume of flow.